﻿A new freshwater amphipod (Arthropoda, Malacostraca, Amphipoda, Gammaridae), Echinogammarusozbeki sp. nov. from the Tomara Waterfall, Turkey

﻿Abstract A new species of freshwater amphipod, Echinogammarusozbekisp. nov., collected from Tomara Waterfall, Gümüşhane province, northeastern Anatolia, is described and illustrated. The new species belongs to the genus Echinogammarus and exhibits characteristic uropod 3 features of that genus. Some of the distinctive features of the Echinogammarusozbekisp. nov. species are a small body length, urosome segments without dorsal elevations, distal end of the peduncle segments of antenna 1 with setae longer than the diameter of the segment, presence of strong spines accompanying setae on both inner and outer margin of exopod, and uropod 3 parviramous.


Introduction
A waterfall is a landform that occurs when water falls down a long or short distance due to the slope of the riverbed. Waterfalls, which are natural wonders, not only possess tourist potential but also serve as subjects for scientific studies in terms of geology, geography, phytology, and zoology. While Türkiye is one of the countries with high potential in terms of natural beauty and biodiversity, there are still deficiencies regarding the biodiversity of water resources (Doğanay 2011). Taxonomy plays a crucial role in determining biological diversity and consequently in the development of conservation plans. The topographic and climatic diversity that Türkiye possesses has led to a high species diversity, providing opportunities for the differentiation of species, especially those with limited mobility (Tavşanoğlu 2016).
Species of the order Amphipoda belonging to marine, freshwater, estuarine, cave, and underground water sources are frequently encountered. Amphipoda are represented by 16 families and 31 genera, and Gammaridae is the most commonly encountered family with 64 species in water resources in Türkiye (İpek and Özbek 2022). Echinogammarus is a genus of Gammaridae with high endemism, mostly inhabiting freshwater and brackish waters; only a few species are marine. The genus Echinogammarus comprises 58 taxa belonging to three main groups: the berilloni group, the simoni group, and the pungens group. Until now, species records belonging to this genus have been recorded from many regions, such as Europe, Algeria, Türkiye, the Iberian Peninsula, and North Africa (Pinkster 1993). According to recent studies, there are seven species belonging to the genus Echinogammarus in Türkiye: E. antalyae G. Karaman, 1971, E. baliki Özbek & Ustaoğlu, 2007, E. foxi (Schellenberg, 1928), E. ischnus Stebbing, 1899, E. trichiatus (Martynov, 1932, E. stocki G. Karaman, 1970, andE. veneris (Heller, 1865). Two of these species (E. antalyae and E. baliki) are endemic (İpek and Özbek 2022).
This study examines the individuals of Echinogammarus collected from Tomara Waterfall, Gümüşhane province, in terms of morphological features. Detailed descriptions and drawings are given of the extremities of the holotype male of a newly identified species, and the morphology of this new species is compared with its relatives.

Materials and methods
Located within the borders of Şiran district of Gümüşhane province, Tomara Waterfall has an area of 70,000 m 2 and flows from an altitude of approximately 1380 m. Its source is underground waters which pass through a deep, narrow valley and flow into Kelkit stream. The habitat is rocky, and vegetation is quite abundant. (Fig. 1a).
The distance between Gümüşhane and Şiran is 101 km, and the distance between Şiran and Tomara Waterfall is 21 km. There is an area available for visitors along the river that continues from the waterfall. To reach the Tomara Waterfall on foot from the lower basin of the river, the distance I approximately 1 km. The waters of this waterfall emerge from a karstic source, and its geological structure consists of layered sedimentary schists, limestone, sandstone, and marl (Doğanay 2011).
Specimens of Echinogammarus were collected with a fine-mesh hand net, fixed in 4% formaldehyde in the field, and later examined and dissected under a stereomicroscope. The body length is measured from the basis of antenna 1 to the basis of the telson, keeping holotype male straight (Hou et al. 2005). Morphological photographs were taken with a digital camera attached to a microscope. The drawings were made with the aid of a drawing tube mounted on a compound microscope. The type specimens have been deposited in the Recep Tayyip Erdoğan University Fisheries Museum. Diagnosis. A small species with kidney-shaped eyes, peduncle segments of antenna 1 bearing a group of long setae distal end, setation of antenna 2  moderate on both peduncular and flagellar segments, urosomites flat, uropod 3 parviramous, inner ramus with 1 or 2 distal spines accompanied by 1 or 2 setae; endopod/exopod ratio 0.21; telson with 1 or 2 setae on outer margin and 1 or 2 setae on the inner surface of each lobe. Anterior and posterior margins of pereopods 5-7 have spines and a few setae.
Antenna 1 (Fig. 3A) longer than half (~0.75) of the body length, setation weak, peduncle segments bear a group of long setae on the distal end; The length of the setae is 1.2 times the diameter of the segment in which they are implanted. The main flagellum with 19 or 20 segments, accessory flagellum 2-or 3-segmented.
Antenna 2 (Fig. 3B) shorter than antenna 1 (0.48 of antenna 1), antennal gland cone straight and reaches to distal end of third peduncular segment, setation moderate on both peduncular and flagellar segments; setae along ventral margins of peduncular segments more than twice as long as diameter of segment; setae on dorsal side of peduncular segments shorter; flagellum with 7 or 8 segments, calceoli absent.
Gnathopod 1 (Fig. 3D): basis with 5 or 6 long setae on both posterior and anterior margins; (up to 2.0 times longer than diameter of segment); ischium and merus with a single group of setae on posterodistal corner; carpus ~0.68 of propodus; propodus with 1 medial palmar spine and 3 palmar angle spines, and a few setae on inner surface; dactylus long, with 1 seta on outer margin.
Gnathopod 2 ( Fig. 3E): basis with long setae on anterior and posterior margins (up to 2.0 times longer than diameter of segment); ischium and merus as on gnathopod 1; carpus ~0.82 of propodus; length of propodus ~0.5 of its width; superior lateral setae bear 3 or 4 groups of setae rows, 1-5 setae in each row; inferior margin bears some setae groups. Propodus palm bear 2 strong and 2 short median palmar spines and short simple setae; without spine on inner surface of propodus.
Pereopod 3 (Fig. 3G): basis bears 2 groups of long setae and 2 setae in each group on posterior margin; 4 or 5 setae on anterior margin; ischium bears 3 or 4 posterodistal seta; merus bears 3 rows of setae and 3 or 6 setae in each row on posterior margin and a setal group at posterodistal tip; 2 rows of spines and setae (order of setas and spins: 1 spine + 1 seta) on anterior margin; 1 strong and 1 small spine and 1 group of long setae in the anterodistal tip; setae longer than diameter of segment. Carpus bears 3 groups of spines and setae on posterior margin (order of setas and spins: 2 spines + 3 setae, 2 spines + 3 or 4 setae, 1 strong spine + 3 setae); bald anterior margin; 1 strong spine and 2 long setae in the anterodistal tip; propodus bear 3 groups of spines and setae on the posterior margin, order of setas and spins 2 spines + 1 seta; bald anterior margin; 3 or 4 setae in the anterodistal tip; 1 plumose seta on dorsal margin; dactylus with 2 simple setae at hinge of nail.
Pereopod 4 (Fig. 6A) shorter than P3; basis bear 4 or 5 long setae on the posterior margin, 1 long seta on anterior margin; 2 setae on anterodistal and posterodistal tip; ischium bears 2 posterodistal setae; merus with 4 groups of setae on posterior margin, 2 spines and 1 seta on anterior margin, 1 strong and 1 small spines and 3 or 4 setae on anterodistal tip; carpus short, with 3 groups of spines and setae on posterior margin (order of setas and spins: 1 spine + 1 seta); bald anterior margin; propodus bear 3 groups of spines and setae on posterior margin; bald anterior margin, 4 or 5 setae in anterodistal; 1 plumose seta on dorsal margin, dactylus with 2 simple setae at hinge of nail.
Pereopod 5 (Fig. 5C): basis with a row of 4 spines on anterior margin; posterior margin of basis slightly convex, serrated, with sequential setae; ischium with 2 spines and 2 setae on anterodistal tip, merus with 3 groups of setae and spines on anterior margin, 2 groups of spines and setae on posterior margin; carpus with 3 groups of spines on anterior tip, 3 groups of spines on posterior margin; propodus with 3 groups of spines on anterior margin, 2 groups of setae on posterior margin; dactylus with 2 simple seta at hinge of nail.
Pereopod 6 ( Fig. 5B): basis convex, without setae on inner surface, 1 spine at posterodistal portion, with sequential setae posterior margin; with 4 sequential spines on anterior margin; ischium with 2 spines and 1 seta on anterodistal tip; carpus with 3 groups of spine + seta combination on anterior margin, 2 groups of spine + seta combination on posterior margin; propodus with 3 groups of spines on anterior margin, 2 groups of setae on posterior margin, 1 plumose seta on dorsal margin; dactylus with 2 simple setae at hinge of nail.
Pereopod 7 (Fig. 5A): basis with a row of 4 spines on anterior margin; serrated; without setae on inner surface; with sequential setae on posterior margin; 1 anterodistal spine; anterodistal corner of ischium with some setae; merus shorter than carpus, 2 groups of small spines on anterior margin, 1 group of spines on posterior margin; some spines and setae on anterodistal and posterodistal corners; carpus 2 with group of small spines on both anterior and posterior margins, some spines and setae on anterodistal and posterodistal corners; propodus same as propodus of pereopod 6, 1 plumose seta on dorsal margin; dactylus with 2 simple seta at hinge of nail.
Telson (Fig. 3C): cleft, each lobe with 1 strong distal spine and 2 or 3 long setae; 1 or 2 setae on outer margin and 1 or 2 setae on inner surface of each lobe.
Pleopods 1-3 (Fig. 6B-D) subequal; peduncle with some setae and 1 or 2 retinacula; rami with 10 or 11 segments and numerous plumose setae. Female (Fig. 2). Body 6.8 mm long. Antenna 1 less setose than that of male, first peduncle segments with long setae on distal portion, with 17-21 segments on flagellum, 2 segments on accessory flagellum. Gnathopod 1 and 2 similar to that of male, setation more intense on propodus, dactyli of gnathopods 1 and 2 long. Uropod 3 similar to that of male, distal part of peduncle with spines; inner and outer margins of outer lobe more densely setose than male outer lobe with row of 2 spine and 5 or 6 setae in each margin. Telson similar to that of male, each lobe with 1 or 2 distal spines accompanied by 1 or 2 setae longer than the spines.
Oostegites present on gnathopod 2 through to pereopod 5. Variability. The number of flagellar segments of Antenna 1 was determined as 16 in six paratype individuals, while Antenna 2 had nine flagellar segments. The number of setae on the inner and outer edges of the exopod varied between three and six.

Discussion
In this study, Echinogammarus ozbeki sp. nov. is compared with species from the family Gammaridae, and their similarities and differences are emphasized. At first glance, E. ozbeki sp. nov. closely resembles Gammarus pageti Mateus & Figure 6. Echinogammarus ozbeki sp. nov. holotype male A pereopod 4 B pleopod 1 C pleopod 2 D pleopod 3 E uropod 1 F uropod 2. Scale bars: 1 mm. Mateus, 1990 andGammarus balcanicus Schäferna, 1923. Gammarus balcanicus is known for its wide distribution range and intraspecific variation. Karaman and Pinkster, (1987) noted that the endopod (uropod 3) of G. balcanicus collected from Keklik (Erzurum province) is relatively short. Echinogammarus ozbeki sp. nov. is similar to G. balcanicus in having spines on the pereopods, relatively little setation on all appendages, and a short endopod. However, it differs from G. balcanicus in the length/width ratio of the telson lobes, the presence of long setae on the peduncular segments of antenna 1, moderate setation on all extremities, long setae on antenna 2, and setae and spines on the outer and inner margin of the exopod 3. Mateus and Mateus (1990) emphasized the short endopod of G. pageti collected from near Maden (Erzurum province). Echinogammarus ozbeki sp. nov. is similar to G. pageti in its exopod/endopod ratio, but differs from by having a parviramous type uropod 3, a row of setae and spines on the gnathopods, and the setation of the mandibular palp.
Echinogammarus ozbeki sp. nov. shows similarities in general body appearance to individuals belonging to the genus Turcogammarus. Turcogammarus aralensis (Uljanin, 1875) and T. spandli (Karaman, 1931) have been recorded from nearby river basins, and one species, T. turcarum (Stock, 1974), has been recorded from Anatolia. E. ozbeki sp. nov. differs from T. turcarum from Mount Ağrı on the Türkiye-Iran border by the absence of long setae on pereopod 7, the presence of short and few setae on the epimeral plate, and the sparser setation of the telson (Karaman 2021). Litorogammarus dursi Marin, Palatov & Copilaș-Ciocianu, 2023, described from the southwestern Caucasus region and the Durso River, and belonging to the Pontocaspian region, exhibits similar characteristics to the new species, such as the exopod/endopod ratio, the absence of carina on metasome segments, and the presence of sequential spines and setae on the exopod of uropod 3 (Marin et al. 2023). However, E. ozbeki sp. nov. differs from L. dursi in having setae on the inner surface of coxal plate 3 absent, less dense setal rows on the mandible and lower lip, curled setae on antenna 2 absent, and a 2-or 3-segmented accessory flagellum. Recent molecular data and studies have confirmed that Chaetogammarus trichiatus and Trichogammarus trichiatus are synonyms (Copilaș-Ciocianu et al. 2023). Chaetogammarus trichiatus (= Echinogammarus trichiatus) is known to occur in Türkiye (İpek and Özbek 2022). The morphological differences between E. ozbeki sp. nov. and E. trichiatus species are compared in the Table 1.
The genus Echinogammarus has been divided into three main groups-E. berilloni group, E. pungens group, and E. simoni group-according to morphological features. Echinogammarus ozbeki sp. nov. differs from the E. berilloni group by the absence of dense setae. Species of the E. berilloni group have a long, dense setae on the different extremites.
Echinogammarus berilloni has dense setae on the metasome and urosome segments. Echinogammarus calvus has long curled setae on the gnathopods. Echinogammarus meridionalis possesses long, straight, and curled setae on antenna 2 and gnathopods. Echinogammarus aquilifer has dense setae only on the flagellum of antenna 2. On the other hand, E. zebrinus bears spines and setae on the urosome and metasome segments. Echinogammarus ozbeki sp. nov. is distinct from other members of the group due to the absence of dense setae or spines on its similar appendages, especially on the metasome segments and the inner surface of the bases of the pereiopods. The shape and setal arrangement of the